How Often Does My Pet Need a Heartworm Test?

It is important for pets to be tested annually for heartworms.

One of the most common questions asked of veterinarians is how often pets need to have a heartworm test.  Both the American Veterinary Heartworm Society and most veterinarians do recommend yearly heartworm testing.   Even though many animal guardians keep their pets on year-round heartworm medication, it is still important to test pets yearly for several reasons.

One of the most important reasons for an annual heartworm test is that, even though most products are highly effective in preventing heartworm infection, there is still no product that is 100% effective.  I have seen many cases in my 20-year veterinary career of pets on year-round heartworm preventative medication that have tested positive for heartworms.  There has also been increasing recent concern about developing heartworm resistance to some of the older products, and until this issue is sorted out, it is still best to have all pets tested every year.   Also in the possibility that a pet is heartworm positive, there can be very occasional severe and even rare fatal reactions should a pet that is positive for heartworms continue to receive monthly preventative.

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  1. Very interesting. And here I thought my vet just wanted the test every year to make a few extra bucks.

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  4. so i always forget when my pet is due for his heart worm test. I found this app which really helps me care for my dog. its called pet minder and is available on android. here is a link

    • I also found an app for MY medicine reminder … and I put the dog’s Trifexis in the same app so it pops up on the 15th of each month. It is called Remind Me …. for my Apple iPod.

  5. My vet recently has insisted that my dog get tested every 6 months for heartworm. Is this really necessary? My dog is on monthly heartworm prevention, but the contention is that if we get a day or days of nice weather, mosquitos may have bitten the dog in between stretches of prevention. Is this just a way of collecting $34.00 ?

  6. I have a Bullmastiff he is 2yrs old and weigh`s 150lbs,I had him on heart worm medication up untill last year but had to stop getting it because I only receive a monthly dissability check and can not afford it.Is there any other means I can do for him that don`t cost so much.I keep up with his check ups when they are due.Do you have any other advice for me to do.I want to keep him healthy but it`s hard to do with a small montly income.

    • Dr. Michael Dym, VMD veterinarianFebruary 9, 2013 at 11:02 pm · Reply

      Heartworm testing is recommended yearly and heartworm medicine is a prescription medicine your vet can write for. You could try herbal heartworm preventative such as quassia bark which you can get from Fiesta pet Deli in Florida which you can find on line

  7. I have wanted to order heartworm meds from
    PetMeds but I can’t find a Vet. that will write me
    a perscription. They all say you have to buy the
    meds from them. Do you know of any Vets. in
    Mobile, Al that will write a perscription? Thanks,

    • Dr. Michael Dym, VMD veterinarianFebruary 10, 2013 at 11:48 am · Reply

      I have a colleague but she practices more holistic vet medicine in Mobile. Her name is Marcia Martin….. She will try and give you other alternatives but could probably write you a prescription.

    • Hi Miriam, if you have recently had your dog tested for heartworms at a reputable Vet and your dog was neg. for heartworms. All you have to do is go online to 1-800-Pet-Meds and place an order for the treatment you want to purchase. There is a section that asks for your zip code and it will list every Vet in a 50 mile radius if you need it to. Just find your vet’s name that done the test…select the box next to his name and office info. PetMeds will contact the vet for test results and THEY will get the prescription FOR YOU!!. It is just that easy. You save money. Usually it ships for free and it will be at your home in 3-4days.


  9. I have checked on heart worm medication between pet meds and my vet.and there is only about a $4 and change difference which is not worth it to me.I thought it would be a big difference the way it`s advertised on TV and my vet is only 5 miles away.

  10. On the first page of this article it says the heartworm pill is 100% effective. On this page, it says that NO pill is 100% effective. The problem is the usual…. greed of the sellers.
    The medication is way too expensive when it doesn’t have to be. The charges for pet products are so out of control it’s not even funny. I’m 66, have taken care of pets all my life and done the ‘right’ thing. Only the right thing becomes more and more expensive, until one has to chose between meds for self or for the dog. The price fixing and price gouging that is going on in America is horrendous. It insinuates itself into everything, and people can no longer afford to treat their pets. Take pigs ears, for example. They’re now at $1.59 each, when they used to be thrown out by butchers, or given away. If you price them by the ounce, they’re more expensive than gold!!! How can they possibly be allowed to charge that kind of money? Where is the competition? Anyone starting a new business and selling them at a quarter a piece would still make a huge profit! Unabashedly overpriced!!!! As our the dog toys and meds. It’s awful out there.

  11. I have had this little Yorker for 2 months. I took him so he wouldn’t have to go to the shelter. I don’t know how old he is, I am guessing about 5 or 6. My vet didn’t put him on heartworm medication and I am thinking he should have. What should I do?

    • Dr. Michael Dym, VMD veterinarianJanuary 23, 2014 at 11:01 pm · Reply

      I would return to vet for heartworm blood test and then if negative, start him on heartworm meds like topical revolution from 1800petmeds

  12. I agree with Linda. The veterinarians are out of control more so than the regular docs who use Medicare patients like ATM machines. I just talked to my vet, and her costs for a heartworm test went up almost double from last year. Now they tell me he doesn’t have to be tested each year if he is on preventive year round, and they have proof that you bought the meds. That’s understandable, but I have 2 dogs and I buy one prescription at a time and they share so I can afford to keep both on this stuff that’s is beginning to cost more than gold. They know you have to have this stuff and they play on your emotionsand stuff their greedy pockets with your limited income bucks. I think we should organize a consumer’s group against the high cost of vet care….I will look for the county animal control dept who offer vaccination clinics.

    • Dr. Michael Dym, VMD veterinarianMay 3, 2014 at 5:32 pm · Reply

      Vaccinations are another money pit unfortunately of veterinary medicine, and are actually not needed in the amounts they are given by most veterinarians. For example, the immunity to core viruses like parvo/distemper lasts for years to life of pet, if vaccinated at 16 weeks of age or older. As for heartworm, as there is no such product that is 100 percent, and there has been recently documented resistance with some heartworms, we still recommend testing annually, especially since this is the American Veterinary Heartworm Society recommendations.

  13. I adopted a stray dog that came to my house a few years ago. She was about eight or nine years old and had heartworms. The vet said she was too old and debilitated to have the treatment. He said she might not survive so he put her on a monthly heartworm prevention and said that it would prevent any new worms from forming and the old ones would eventually die. Within a few months the coughing stopped and five years later she’s doing quite well. Since then I don’t get the heartworm test for any of my four dogs but on the last visit I was told I couldn’t get medication without the test. That test is the biggest rip off. Forty dollars for each dog each year for what??? If they have heartworms I would still not put them through the treatment because it’s dangerous to them. Is there really a LAW in Texas that says you have to have the test to get meds?

    • Dr. Michael Dym, VMD veterinarianAugust 6, 2014 at 7:49 pm · Reply

      No law Sharon, but most vets are following the recommendations of the American Veterinary Heartworm society on annual testing. Also some of the preventatives are no longer 100 percent effective anymore, due to some emerging heartworm resistance being seen; thus the annual testing.

    • Sharon, if you live near Waco, the Animal Birth Control Clinic does heartworm tests for $10.

  14. My 11-yr. old Cocker Spaniel had surgery on his gums 2 months ago to remove a growth. The biopsy first said the growth was a fibromatous & ossifying epulis. Then after the removal, the biopsy said it could be a fibrosarcoma or a acanthomatous epulis – the pathologists couldn’t agree. I was told to be vigilant for the next 5 months to make sure the growth doesn’t reappear. I feel wary about giving my dog Revolution heartworm preventative since no one is really sure what this growth was. Also, the vet says there seems to be a slight enlargement in a lymph node, but this could be from the sebaceous cyst on his ear or gingivitis. Do you think it would be safe to start Revolution again? My vet thinks it’s OK, even though my dog has not been given Revolution for 2 months. Just wanted your opinion. Thanks!

    • Dr. Michael Dym, VMD veterinarianSeptember 12, 2014 at 4:22 pm · Reply

      HI Mindy. While topical revolution is an excellent product for flea and heartworm control, any topical and/or oral pesticide may have the potential to aggravate his body’s detoxifying mechanisms, when used chronically over time, which can be important with case that we are not sure about cancer in the mouth. I think revolution is one of the safer of the pesticides we use, however if you are very concerned then using natural flea/heartworm control may be an off label option for you. See the website for some suggestions

  15. I am on SS and thus get a check once a month that allows me to just make it thru the month. My problem is my check isn’t always on the same date each month. I’ve had my dog on monthly heartworm/flea meds. My vet insists that if I am even just a few days past the due date on the dogs meds that he has to have the heartworm test done all over again before I can get the next dose. Is this accurate? I can’t afford to buy more than one month at a time and the testing is going to be getting pretty expensive at this rate. I have to do what’s best for my dog, though. Your input would be much appreciated. Do the monthly doses ‘have’ to be fairly exact as to date administered?

    • Dr. Michael Dym, VMD veterinarianOctober 23, 2014 at 10:31 pm · Reply

      Hi Julee. Actually there is several week safety factor for many heartworm preventatives. For example, ivermectin, the main ingredient in heartguard or iverhart, protection lasts up to at least 6 weeks and possibly up to 3 months. So no worry about being EXACTLY on time each month

  16. Hi, my 5 year old labradour, was tested for heartworm last month came back neg. They want to test him again in april 2016 because apparently he is 105 pounds and they said i did not give the right dosage for his weight. I gave him heartgard for up to 100 pounds but i did not give him heartgard blue for 25 pounds.Now would that have a made a difference. Is there a chance that he could develop heartworms in the next 6 months. I give him the exact dosage now. The brown and the blue.And would the heartgard kill the larve.

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